Methods and apparatus to determine an operational status of a device

ABSTRACT

Methods, apparatus, systems and articles of manufacture are disclosed to determine an operational status of a device. An example method includes determining, with a processor, a first multi-dimensional measurement of a first magnetic field generated by a power cord to supply power to a device; and determining, via the processor, an operational status of the device based on the first multi-dimensional measurement.

FIELD OF THE DISCLOSURE

This disclosure relates generally to audience measurement, and, moreparticularly, to determining an operational status of a device.

BACKGROUND

Audience measurement of media, such as content, advertisements, etc.presented via a computer, tablet, smartphone, television and/or radio,is often carried out by monitoring media exposure of panelists that arestatistically selected to represent particular demographic groups.Audience measurement companies, such as The Nielsen Company (US), LLC,enroll households and/or persons to participate in measurement panels.By enrolling in these measurement panels, the households and/or personsagree to allow the corresponding audience measurement company to monitortheir exposure to media presentations, such as media output via atelevision, a radio, a computer, etc. Using various statistical methods,the media exposure data collected from the panel is processed todetermine the size and/or demographic composition of the audience formedia of interest. The audience size and/or demographic informationis/are valuable to, for example, advertisers, broadcasters, contentproviders, manufacturers, retailers, product developers, etc. Forexample, audience size and/or audience demographic compositioninformation may be a factor in the placement of advertisements, invaluing commercial time slots during particular programs and/orgenerating ratings for media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial view of an example power cord and an example magneticfield caused by electric current in the power cord.

FIG. 2A illustrates a prior art sensor to measure a magnetic field.

FIG. 2B illustrates the prior art sensor of FIG. 2A non-tangentiallyaligned with the magnetic field surrounding the power cord of FIG. 1.

FIG. 2C illustrates the prior art sensor of FIG. 2A tangentially alignedwith a portion of the magnetic field surrounding the power cord of FIG.1.

FIG. 3 is an isometric view of the example power cord of FIG. 1 in atwisted configuration.

FIG. 4 illustrates an example system in which an example power detectorconstructed in accordance with the teachings of this disclosure is usedto detect the operational status of a media presentation device.

FIG. 5 is a block diagram of an example implementation of the examplepower detector of FIG. 4.

FIG. 6 illustrates an example sensor that may be utilized in the examplepower detector of FIGS. 4 and/or 5.

FIG. 7 illustrates an example magnetic field environment in which theexample power detector of FIG. 4 may be used.

FIG. 8 is a block diagram representative of an example implementation ofan example comparator of the example power detector of FIGS. 4 and/or 5.

FIG. 9 is a flowchart representative of example machine readableinstructions that may be executed to implement the example powerdetector of FIG. 5.

FIG. 10 is a flowchart representative of example machine readableinstructions that may be executed to implement one or more examplesensor(s) of FIG. 5 and/or the example sensor of FIG. 6.

FIG. 11 is a flowchart representative of example machine readableinstructions that may be executed to implement the example comparator ofFIG. 8.

FIG. 12 is a block diagram of an example processing platform capable ofexecuting the machine readable instructions of FIGS. 9, 10, and/or 11 toimplement the example power detector of FIGS. 4 and/or 5 and/or theexample comparator of FIG. 8.

DETAILED DESCRIPTION

When conducting audience measurement studies it may be useful to monitorthe operational status of, for example, a media presentation device. Forexample a set-top box outputs media regardless of the operational statusof a connected television, it may be useful to detect the operationalstatus of the television to determine whether the media output by theset-top box is actually being presented, and thus, likely exposed to anaudience. The operational status of an electric device may be detectedby monitoring for electric current in a power cord connected to thedevice. Electric current flowing through a conductor induces a magneticfield. Detection and/or measurement of the magnetic field may be used todetermine an operational status (e.g., an on/off state, an operatingmode, etc.) of a device drawing the electric current (e.g., via a powercord). For example, when a power cord connected to a device is pluggedinto a power source (e.g., an electrical outlet providing 120 V AC) andthe device is powered on, the device draws electric current from thepower source through the power cord inducing a magnetic field around thepower cord. Accordingly, it can be inferred that the device is poweredon when a magnetic field caused by the electric current is measured inthe vicinity of the power cord and/or in the vicinity of the device. Onthe other hand, it can be inferred that the device is powered off when amagnetic field expected to be caused by the electric current is notdetected and/or not measured to have an expected magnitude (e.g., athreshold magnitude) in the vicinity of the power cord and/or in thevicinity of the device. Based on the operational status, an audiencemeasurement entity may determine when and/or whether an audiencemeasurement should be made. For example, an operational status mayindicate that a media presentation device is powered on and thereforepresumed to be presenting media.

Example methods, apparatus, and/or articles of manufacture disclosedherein utilize a multi-dimensional power detector to detect a magneticfield and determine an operational status of a device. An examplemulti-dimensional power detector disclosed herein detects components ofa magnetic field near a wire in three dimensions. The example powerdetector determines if a resulting magnitude of the magnetic fieldexceeds a threshold to determine if electricity is flowing in the wire.Based on the determination of flowing electricity, the example powerdetector determines an operational status of a device attached to thewire (e.g., a television or other media presentation device).

FIG. 1 is an axial view of an example power cord 100. In examplesdisclosed herein, the power cord 100 supplies electricity to an exampleelectronic device (e.g., a television, set top box, a game console,etc.). The example power cord 100 includes a first wire 102 and a secondwire 104. In the example of FIG. 1, the wires 102, 104 (e.g.,conductors) are conductively insulated from each other and aresurrounded by an example sheath 110 (e.g., an insulator). In theillustrated example, electric current flows through the wires 102, 104(designated by a “•” in the wire 102 representing current coming out ofthe page toward the reader and an “X” in the wire 104 representingcurrent going into the page away from the reader of FIG. 1) when theelectronic device connected to the power cord 100 is drawing electricity(i.e., when it is powered on). In the illustrated example of FIG. 1, theelectric current in the power cord 100 induces an example magnetic field120.

FIG. 2A illustrates a magnetic head 200 that may be used to detect amagnetic field (e.g., the magnetic field 120). The magnetic head 200uses an active sensor 202 that detects a magnetic field 204 that istangential to the active sensor 202. For example, the magnetic head 200may be an audio magnetic head such as one that was designed to readmagnetic cassettes. When, the magnetic head 200 is placed in a magneticfield such that the active sensor 202 is tangential in space with themagnetic field 204, the magnetic field 204 may be sensed and/ormeasured. Accordingly, the magnetic head 200 measures only a scalar, onedimensional value of a magnetic field that is tangential to an activesensor of the magnetic head 200. However, because the active sensor 202of the example magnetic head 200 can only measure a magnetic field 204that is tangential to the active sensor 202, the magnetic head 200 mustbe carefully aligned to detect the magnetic field 204.

FIG. 2B illustrates the example magnetic head 200 placed in the magneticfield 120 surrounding the example power cord 100 of FIG. 1. However, inthe example of FIG. 2B, the magnetic head 200 is not tangentiallyoriented with the magnetic field 120. Accordingly, the active sensor 202cannot accurately detect the magnetic field 120 and/or make an accuratemeasurement of the magnetic field 120. For example, due to themisalignment, the magnetic head 200 may not detect any measureablemagnetic field despite the presence of the magnetic field 120.

FIG. 2C illustrates proper tangential alignment of the example magnetichead 200 and the magnetic field 120 such that the magnetic field 120 canbe detected and/or measured by the magnetic head 200. As shown in theexample of FIG. 2C, the magnetic field represented by arrow 204 isimmediately adjacent the magnetic head 200 and, thus, can be sensed.Achieving the proper alignment illustrated in FIG. 2C may requireseveral iterations of manual alignment adjustments. For example,occasionally the power cord 100 of FIGS. 1, 2B, and/or 2C is twistedand/or moved after placement of the magnetic head 200 as shown in FIG.3. In some examples, the power cord 100 is manufactured such that thewires 102, 104 internal to the power cord 100 are in a twistedconfiguration (e.g., the wires 102, 104 internal to the power cord 100are twisted around each other). When the power cord 100 is twisted orotherwise not uniform, the magnetic field 120 induced by the currentflowing in the example power cord 100 follows the orientation of thewires. Accordingly, to accurately sense the magnetic field 120, anoperator would need to properly realign the magnetic head 200 of FIGS.2A-2C such that the active sensor 202 is tangentially aligned with thetwisted magnetic field.

Methods, articles of manufacture, and/or apparatus to determine anoperational status of a device are disclosed herein. An example methodincludes measuring a first magnetic field associated with a device bydetermining a first multi-dimensional vector indicative of the firstmagnetic field and determining an operational status of the device basedon the vector. Some example methods, apparatus, and/or articles ofmanufacture also include measuring a second magnetic field to determinea second magnetic field vector and comparing the second magnetic fieldvector to the first magnetic field vector to determine an operationalstatus of a device.

FIG. 4 illustrates an example environment 400 in which an example powerdetector 410 constructed in accordance with the teachings of thisdisclosure is utilized to detect the operational status of a mediapresentation device 402. The example environment 400 of FIG. 4 includesan example media presentation device 402, an example set top box 404,and an example power outlet 406. In the example of FIG. 4, an examplefirst meter 408 and an example second meter 420 are present forcollecting audience measurement data. In the illustrated example of FIG.4, the media presentation device 402 presents media provided via the settop box 404 and/or other media source(s) (e.g., a game console, anantenna, a mobile device (e.g., a smartphone, tablet computer, iPad,etc.) etc.). The example media presentation device 402 (e.g., atelevision, a monitor, etc.) of FIG. 1 is electrically connected to thepower outlet 406 via an example power cord 100, which may be similar tothe power cord 100 of FIGS. 1 and/or 3. The example outlet 406 is inelectrical communication with a source of commercial power. When in thepowered on state, the example media presentation device 402 of FIG. 4draws electricity from the power outlet 406 (e.g., an outlet supplying120 VAC or any other type of electricity) via the power cord 100.

The example power detector 410 of FIG. 4 detects and/or measures amagnetic field (e.g., the magnetic field 120 of FIG. 1) and/or anelectric current associated with the magnetic field in accordance withthe teachings of this disclosure. In the illustrated example of FIG. 4,the power detector 410 determines an operational status (e.g., poweredon, powered off on standby, in sleep mode, etc.) based on magneticfields detected and/or measured within the system 400 (e.g., around thepower cord 100). Although this disclosure refers to measuring magneticfield, it will be understood that measuring a magnetic field is ameasure of the associated electric current and measuring an electriccurrent is a measure of the corresponding magnetic field. Thus, whenevermeasuring a magnetic field is mentioned, it will be understood this canbe done by measuring the corresponding electric current and vice versa.The example power detector 410 of FIG. 4 constructed in accordance withthe teachings of this disclosure may be used as an alternative to themagnetic head 200 of FIGS. 2A-2C to determine the operational status ofthe media presentation device 402. In some examples, the power detector410 detects and/or measures a magnetic field around the power cord 100of the media presentation device 402, while in other examples, the powerdetector 410 detects and/or measures a magnetic field around a powercord of another device, such as the set top box 404 and/or other type ofmedia presentation device. Additionally or alternatively, the powerdetector 410 (or a second power detector) may detect and/or measuremagnetic field(s) around an audio cable and/or video cable connected toa media presentation device and/or connected to any other type ofcomponents to determine the operational status of the correspondingmedia presentation device.

The example first meter 408 of FIG. 4 is an example audience measurementdevice to measure the operational status of the media presentationdevice 402 and to transmit collected operational status information to ameasurement entity. For example, the first meter 408 may uploadoperational status information reflecting the operational status of themonitored device via a network associated with the environment 400. Inthe illustrated example of FIG. 4, the power detector 410 providesoperational status information reflecting the operational status of themonitored media presentation device 402 to the first meter 408. Thefirst meter 408 of FIG. 4 stores the operational status information in adatabase of the first meter 408 until the operational status informationis provided to the example audience measurement entity. In response toreceiving operational status information indicating that the mediapresentation device 402 is powered on, the example first meter 408 sendsa signal to the example second meter 420 (e.g., a personal meter, aportable meter, an on-device meter (ODM) of a mobile device, and/orother metering device) to indicate that the second meter 420 is to beginmeasuring audience information. In some examples, in response todetermining the operational status information, the second meter 420captures media identification information accompanying media presentedvia the media presentation device 402 to measure an audience of thepresented media. For example, the second meter 120 may capturewatermarks and/or codes associated with the presented media and/orgenerate signatures associated with the presented media. In someexamples, the power detector 410 provides operational status informationto the second meter 420 (e.g., via a wireless communication) and/or thefirst meter 408 is eliminated and its function is performed by thesecond meter 420. In some examples, the first meter 408 and the secondmeter 420 of FIG. 4 perform the same audience measurement operations.Accordingly, the example first meter 408 additionally or alternativelymay capture media identification information (e.g., watermarks, codes,signatures, metadata, etc.).

In some examples, the first meter 408 and/or the second meter 420 ofFIG. 4 detects media by capturing and/or detecting media identificationinformation (e.g., watermarks, signatures, codes, etc.) associated withthe presented media and embedded in audio and/or video of the media.Audio watermarking is a technique used to identify media such astelevision broadcasts, radio broadcasts, advertisements (televisionand/or radio), downloaded media, streaming media, prepackaged media,etc. Existing audio watermarking techniques identify media by embeddingone or more audio codes (e.g., one or more watermarks), such as mediaidentifying information and/or an identifier that may be mapped to mediaidentifying information, into an audio and/or video component. In someexamples, the audio or video component is selected to have a signalcharacteristic sufficient to hide the watermark. As used herein, theterms “code” or “watermark” are used interchangeably and are defined tomean any identification information (e.g., an identifier) that may beinserted or embedded in the audio or video of media (e.g., a program oradvertisement) for the purpose of identifying the media or for anotherpurpose such as tuning (e.g., a packet identifying header). As usedherein “media” refers to audio and/or visual (still or moving) contentand/or advertisements. To identify watermarked media, the watermark(s)are extracted and used to access a table of reference watermarks thatare mapped to media identifying information.

FIG. 5 is a block diagram of an example implementation of the examplepower detector 410 of FIG. 4. The example power detector 410 of FIG. 5includes an example power sensor 502, an example environment sensor 504,an example comparator 506, and an example status analyzer 510. Theexample power detector 410 of FIG. 5 determines a magnetic fieldstrength near the power sensor 502 (e.g., the magnetic field 120surrounding the power cord 100) to determine the operational state of adevice connected to the power cord 100.

The example power sensor 502 and the example environment sensor 504 ofFIG. 5 respectively measure respective magnetic fields for a period oftime (e.g., 0.5 seconds). The example power sensor 502 and the exampleenvironment sensor 504 of FIG. 5 detect and/or measure a respectivemagnetic field at the physical location of the corresponding sensors502, 504 by sampling the magnetic field. For example, the power sensor502 and the environment sensor 504 may measure respective magneticfields at a given sampling frequency (e.g., 55 Hz). Accordingly, aplurality of samples (e.g., 11 samples for 50 Hz AC and for 60 Hz ACwaveform, etc.) may be measured by the sensors 502, 504 to obtain asuitable magnetic field measurement. In such examples, the sensors 502,504 measure a full sinusoidal waveform (e.g., one sampled sine period)of the measured magnetic fields.

In some examples, the power sensor 502 is implemented via a plurality ofpower sensors oriented such that a multi-dimensional measurement can bemade from the plurality of power sensors (e.g., three sensors havedifferent physical orientations to measure three components of amagnetic field). The measurement information of the power sensor 502 isprovided to the comparator 506 for analysis.

In some examples, the environment sensor 504 is implemented via aplurality of environment sensors oriented such that a multi-dimensionalmeasurement can be made from the plurality of environment sensors (e.g.,three sensors have different physical orientations to measure threecomponents of a magnetic field). The measurement information of theenvironment sensor 504 is provided to the comparator 506 for analysis.

In the illustrated example of FIG. 5, the power sensor 502 and theenvironment sensor 504 are implemented by similar devices (e.g., thepower sensor 502 and the environment sensor 504 are implemented by asame model magnetometer from a same manufacturer). Each of the examplepower sensor 502 and the example environment sensor 504 of FIG. 5 areimplemented by magnetometers (e.g., a vector magnetometer, amagnetoresistive magnetometer, etc.) that respectively measure magneticfields in multiple dimensions surrounding the corresponding sensors 502,504. Accordingly, the power sensor 502 multi-dimensionally measures themagnetic field near the power cord 100 and the environment sensor 504multi-dimensionally measures the magnetic field of the environment.Freescale® MAG3110 sensors may be used to implement the example sensors502, 504. For example, each of the sensors 502, 504 may respectivelymeasure three dimensional (3D) components (e.g., an x-axis component, ay-axis component, and a z-axis component) of the respective magneticfields.

FIG. 6 illustrates an example 3D measurement collected by one of thesensors 502, 504. An example sensor 600 (which may be used to implementeither of the sensors 502, 504 of FIG. 5) illustrated in FIG. 6 measuresthree magnetic field components 602 (x, y, z) of a magnetic fieldsurrounding the sensor 600. In the illustrated example, the measuredmagnetic field components 602 are used to determine a magnetic fieldvector 604, which represents a magnitude and a direction of the measuredmagnetic field. Because the sensor 600 can measure the magnetic fieldsurrounding the sensor in multiple dimensions (e.g., 3D) and determine amagnetic field vector of the magnetic field, the physical orientation ofthe sensor does not need to be tangential to the magnetic field tomeasure that magnetic field. In contrast, referring back to FIGS. 2A-2C,the magnetic head 200 measures only a scalar, one dimensional value of amagnetic field that is tangential to an active sensor of the magnetichead 200.

Returning to the illustrated example of FIG. 5, the power sensor 502 isphysically located proximate to the power cord 100 such that a magneticfield induced by electricity flowing through the power cord 100 isdetected. For example, the power sensor 502 and/or the power cord 100 ofthe illustrated example are within 5 millimeters of one another. Inother examples, the power sensor 502 and the power cord 100 may be morethan 5 millimeters apart (e.g., depending on the specifications of thepower sensor 502). For illustrative purposes, dashed lines runningthrough the power sensor block 502 represent example wires 102, 104 ofthe example power cord 100 of FIG. 4 running near or proximate the powersensor 502. The illustrated example wires 102, 104 are not components ofthe example power detector 410 of FIG. 5.

The example environment sensor 504 of FIG. 5 is physically located at adistance from the power cord 100 such that the magnetic field caused bythe electricity flowing through the power cord 100 is essentially notdetected (e.g., less than a threshold amount of the field is detected)and/or not included in the magnetic field measured by the environmentsensor 504. As used herein, a first magnetic field essentially does notinclude a second magnetic field when the second magnetic field isimmeasurable by a sensor (e.g., the environment sensor 504) within thefirst magnetic field, is not detectable by a sensor within the firstmagnetic field, has a magnetic field strength below a detectablethreshold of a sensor when the sensor measures the first magnetic field,etc. For example the environment sensor 504 may be relatively distant(e.g., more than 5 millimeters, more than 10 millimeters, etc.) from thepower sensor 502 and/or the power cord 100. FIG. 7, as described infurther detail below, further illustrates this concept.

In the illustrated example, magnetic field measurements from the powersensor 502 and the environment sensor 504 are used to determine amagnetic field from the power cord 100. The example magnetic fieldmeasurements may be determined from a plurality of magnetic fieldmeasurement samples (e.g., 99 samples). The environment sensor 504 ofthe illustrated example measures an environment magnetic field of theenvironment of the power detector 410. For example, the environmentmagnetic field may be caused by the magnetic field of Earth, by otherdevices (e.g., the media presentation device 402, the set top box 404,the meter 408 of FIG. 4), and/or by other components (e.g., elements oflogic circuits, processors, etc.) of the power detector 410. On theother hand, the example power sensor 502 measures that includes both theenvironment magnetic field and a magnetic field from the power cord 100.By subtracting the vector representation of the environment magneticfield from the magnetic field measured by the power sensor 502, themagnetic field generated by the power cord 100 can be determined. Anexample system in which an environment measurement is utilized isdescribed in conjunction with FIG. 7.

The example power sensor 502 and the example environment sensor 504 ofFIG. 5 provide their respective magnetic field measurements to theexample comparator 506. Each of the magnetic field measurements includemulti-dimensional magnetic field measurement components (e.g., valuesfor each of the magnetic field components 602 (x, y, z)) that may berepresented by a vector. In some examples, the magnetic fieldmeasurements may be a scalar magnitude and a direction, etc. In someexamples, the example comparator 506 compares one or more magnetic fieldmeasurement vector(s) received from the power sensor 502 and/or theenvironment sensor 504 by subtracting the magnetic field measurementvector(s) of the environment sensor 504 from one or more correspondingmagnetic field measurement vector(s) of the power sensor 502. In otherexamples, the comparator 506 subtracts magnetic field measurementcomponents received from the environment sensor 504 from correspondingmagnetic field measurement components received from the power sensor 502on a dimension by dimension level. For example, in some such examples,an x-component of a vector from the environment sensor 504, issubtracted from an x-component of a vector from the power sensor 502, ay-component a of vector from the environment sensor 504 is subtractedfrom a y-component of a vector from the power sensor 502, and az-component of a vector from the environment sensor 504 is subtractedfrom a z-component of a vector from the power sensor 502. The examplecomparator 506 of the illustrated example determines a device magneticfield vector measurement from the difference calculated from thecorresponding component values.

In some examples, the comparator 506 performs a sample harmonization ofa plurality of the compared magnetic field measurement samples to verifya magnetic field measurement. As an example, the sensors 502, 504measure the magnetic field at an example sampling rate of 55 Hz for aperiod of time (e.g., 1.8 seconds) to generate the plurality of magneticfield measurement samples. The example comparator 506 subtracts themagnetic field measurement samples of the environment sensor 504 fromthe magnetic field measurement samples of the power sensor 502 asdescribed above. Accordingly, at a sampling rate of 55 Hz for electriccurrent having a frequency of 50 Hz or 60 Hz and flowing through thepower cord 100, the comparator 506 measures at least eleven samples toprovide enough samples for a magnetic field measurement, which, in thisexample, is at least one full sinusoidal period of the AC electriccurrent. Furthermore, during an example 1.8 second time period, thesensors 502, 504 may measure nine 50 Hz or 60 Hz sinusoidal periods(from 99 samples). In some examples, the comparator 506 averages thesinusoidal periods and/or corresponding magnetic field measurementsamples of the sinusoidal periods to determine a magnetic fieldmeasurement. The example comparator 506 may adjust (e.g., in response toa user input or other settings) a number of magnetic field measurementsamples taken and/or a length of the period of time used to measure themagnetic field. For example, if the operational status of a device is tobe determined more frequently, less magnetic field measurement samplesand/or a shortened period of time may be used to measure the magneticfield near the power cord 100. On the other hand, to increase accuracy,more magnetic field measurement samples may be taken or a longer periodof time may be used to measure the magnetic field near the power cord100.

In some examples, if the magnetic field measurement indicates anunexpected measurement (e.g., due to a false measurement, due to noise,etc.), then the comparator 506 may determine that the magnetic fieldmeasurement is not to be used to determine the operational status of thedevice. Additionally or alternatively, the comparator 506 of FIG. 5performs a root mean square (RMS) analysis of the calculated devicemagnetic field vectors for magnetic field measurement samples resultingfrom subtracting the vectors measured by the environment sensors 504from the vectors measured by the power sensor 502 (e.g., eleven for 50Hz and 60 Hz AC). For example, for 11 periods of 50 Hz or 60 Hz AC, theRMS calculation for an x-coordinate component of the magnetic fieldmeasurement vector may be:

$x_{{RM}\; S} = \sqrt{\frac{1}{11}\left( {X_{1}^{2} + X_{2}^{2} + \ldots + X_{11}^{2}} \right)}$

where x_(n) is a sample x-coordinate component of a magnetic fieldmeasurement. The example comparator 506 performs the RMS analysis todetermine a magnitude of a vector value of a device magnetic field. Insome examples, the comparator 506 filters the RMS value using aninfinite impulse response (IIR) filter to lower value fluctuations andrelatively maintain an accurate device magnetic field measurement forlow electric current. Ultimately, in the illustrated example of FIG. 5,the comparator 506 determines the vector value of the device magneticfield induced by electricity in the power cord 100 (e.g., exclusive ofthe environment magnetic field).

In to the illustrated example of FIG. 5, the physical orientation of thepower sensor 502 and the environment sensor 504 are the same orsubstantially the same. For example, one or more axis (axes) of thepower sensor 502 is aligned (e.g. planar) with corresponding axis (axes)of the environment sensor 504. Thus, in the illustrated example, thepower sensor 502 and the environment sensor 504 are oriented in in thesame manner in one or more same plane(s). In some examples, when thepower sensor 502 and the environment sensor 504 do not have the sameorientation (e.g., one or both of the sensors 502, 504 are off-axis, thesensors 502, 504 are not in a same plane, etc.), the comparator 506 ofthe power detector 410 may perform a calibration technique to accountfor the different orientation. For example, the comparator 506 maydetermine the physical orientation of the power sensor 502 and theenvironment sensor 504 and adjust the respective measurements form thesensors 502, 504 based on the orientations of the sensors. In someexamples, the comparator 506 may calculate an average value of amagnetic field measurement (e.g., a sinusoidal period) and if a non-zerovalue is found, the non-zero value may be subtracted from the magneticfield measurement samples (e.g., to remove a DC field and obtainrelatively pure AC field values).

In the illustrated example of FIG. 5, the comparator 506 provides thedevice magnetic field measurements to the status analyzer 510. Theexample status analyzer 510 of FIG. 5 determines an operational statusof a device (e.g., the media presentation device 402 of FIG. 4) based onthe device magnetic field measurement. In some examples, the statusanalyzer 510 determines that the operational status of the device ispowered on when a vector value of the device magnetic field measurementsatisfies a threshold. For example if a magnitude of the vector valueassociated with the magnetic field 120 from the power cord 100 of FIG. 4satisfies a first threshold (e.g., is equal to or above a given value),the status analyzer 510 determines that the media presentation device402 is powered on. In some examples, the status analyzer 510 determinesthat the operational status of the device is powered off when a devicemagnetic field is not detected and/or when a vector value of the devicemagnetic satisfies a second threshold (e.g., a magnitude of the devicemagnetic field vector is below the second threshold). In some examples,the status analyzer 510 determines an operational status (e.g., standby, sleep mode, etc.) when the vector value of the device magnetic fieldsatisfies two or more thresholds (e.g., is above the second threshold ofthe above example and below the first threshold of the above example).For example, the status analyzer 510 may determine that the mediapresentation device 402 is in a sleep mode when a magnitude of thevector value is between the first threshold and the second threshold.

In some examples, the status analyzer 510 includes an interface tocommunicate with one or more external devices (e.g., the first meter408, the second meter 420, etc.). In some examples, the status analyzer510 is responsive to request (e.g., from the meters 408, 420) todetermine an operational status of a device (e.g., the mediapresentation device 402). In some such examples, the status analyzer 510prompts the power sensor 502 and/or the environment sensor 504 to takerespective magnetic field measurements at the respective locations ofthe sensors 502, 504. In some examples, the status analyzer 510 providesoperational status information indicating the operational status of ananalyzed device (e.g., the media presentation device 402) to one or moreexternal devices, such as the meters 408, 420 and/or other devices incommunication with the power detector 410. In some examples, the statusanalyzer 510 transmits the operational status information through acommunication network (e.g., the Internet or other network) to a datacollection facility (e.g., a data server managed by an audiencemeasurement entity).

While an example manner of implementing the power detector 410 of FIG. 4is illustrated in FIG. 5, one or more of the elements, processes and/ordevices illustrated in FIG. 5 may be combined, divided, re-arranged,omitted, eliminated and/or implemented in any other way. Further, theexample power sensor 502, the example environment sensor 504, theexample comparator 506, the example status analyzer 510 and/or, moregenerally, the example power detector 410 of FIG. 5 may be implementedby hardware, software, firmware and/or any combination of hardware,software and/or firmware. Thus, for example, any of the example powersensor 502, the example environment sensor 504, the example comparator506, the example status analyzer 510 and/or, more generally, the examplepower detector 410 could be implemented by one or more analog or digitalcircuit(s), logic circuits, programmable processor(s), applicationspecific integrated circuit(s) (ASIC(s)), programmable logic device(s)(PLD(s)) and/or field programmable logic device(s) (FPLD(s)). Whenreading any of the apparatus or system claims of this patent to cover apurely software and/or firmware implementation, at least one of theexample power sensor 502, the example environment sensor 504, theexample comparator 506, and/or the example status analyzer 510 is/arehereby expressly defined to include a tangible computer readable storagedevice or storage disk such as a memory, a digital versatile disk (DVD),a compact disk (CD), a Blu-ray disk, etc. storing the software and/orfirmware. Further still, the example power detector 410 of FIG. 4 mayinclude one or more elements, processes and/or devices in addition to,or instead of, those illustrated in FIG. 5, and/or may include more thanone of any or all of the illustrated elements, processes and devices.

FIG. 7 illustrates an example transverse view of an example powerdetector 410, which may be implemented by the power detector 410 ofFIGS. 4 and/or 5, and an axial view of the example power cord 100. Inthe illustrated example of FIG. 7, a device magnetic field 700 isinduced by electricity flowing through the power cord 100 and anenvironment magnetic field 710 is caused by environmental effects (e.g.,the earth magnetic field, a magnetic field from other devices not undermeasurement near the power detector 410, a magnetic field induced byother components of the power detector 410, etc.). In the illustratedexample of FIG. 7, the power cord 100 is positioned in an example slot730 of an example housing 740 of the power detector 410. The exampleslot 730 is positioned above the power sensor 502 and may be used tohold the example power cord 100 in position adjacent the power sensor502. Accordingly, the power sensor 502 is located physically near thepower cord 100 and the environment sensor 504 is located relativelydistant from the power sensor 502 and/or the power cord 100. As shown inthe illustrated example, the power sensor 502 is located within thedevice magnetic field 700 induced by the electricity flowing through thepower cord 100 (e.g., a magnetic field similar to the magnetic field 120of FIGS. 1, 2B, and/or 2C) and is also located in the environmentmagnetic field 710. In the illustrated example of FIG. 7, theenvironment sensor 504 is physically located within the environmentmagnetic field 710 and outside of the device magnetic field 700.Therefore, in the illustrated example of FIG. 7, the power sensor 502 isable to detect and/or measure the device magnetic field 700 and theenvironment sensor 504 is not influenced (e.g., is influenced to a smallextent that can be ignored for practical purposes) by the devicemagnetic field 700.

In the illustrated example of FIG. 7, the power sensor 502 samples themagnetic field 700 near the power cord 100 and the environment sensor504 samples the magnetic field 710 of the environment. Accordingly, asdescribed above, the comparator 506 subtracts the magnetic fieldmeasurements of the magnetic field 710 (from the environment sensor 504)from the magnetic field measurements of the magnetic field 700 (from thepower sensor 502) to determine the magnetic field induced by theelectric current flowing through the power cord 100. The examplecomparator 506 of the example power detector 410 performs a sampleharmonization of the magnetic field measurement samples from the powersensor 502 and the environment sensor 504. Additionally oralternatively, the comparator 506 performs an RMS calculation of thecompared measurement vectors from the resulting subtraction.

FIG. 8 is a block diagram of an example comparator 506 receivingmeasurement information from the example sensors 502, 504. The examplecomparator 506 of FIG. 8 may be used to implement the comparator 506 ofFIG. 5. The example comparator 506 of FIG. 8 includes an examplesubtractor 810, an example sample harmonizer 830, an example RMScalculator 840, and an example measurement output 850.

The example subtractor 810 of FIG. 8 subtracts the magnetic fieldmeasurement samples received from the environment sensor 504 from themagnetic field measurement samples received from the power sensor 502 todetermine device magnetic field measurement samples representative ofthe device magnetic field measurement (e.g., a magnetic fieldmeasurement excluding the environment magnetic field measurement).

The example sample harmonizer 830 of FIG. 8 performs a sampleharmonization of the device magnetic field measurement samples asdisclosed herein. Accordingly, the sample harmonizer 830 averagescorresponding sample values of the sinusoidal periods to determine afinal device magnetic field measurement vector (e.g., a full averagedsinusoidal period from measured sinusoidal periods). The example RMScalculator 840 performs a RMS calculation of the resulting measurementvector over the samples of each dimension of the vector to determine amagnitude of the measurement vector. The example measurement output 850indicates a magnetic field strength based on the magnitude of the devicemagnetic field vector. The example measurement output 850 provides thedevice magnetic field vector to the status analyzer 510 of FIG. 5.Accordingly, the status analyzer 510 of FIG. 5 may compare the magneticfield strength to a threshold to determine an operational status of adevice (e.g., the media presentation device 402 of FIG. 4) based on themeasurements of the comparator 506 of FIG. 8.

A flowchart representative of example machine readable instructions forimplementing the power detector 410 of FIGS. 4 and/or 5 is shown in FIG.9. In this example, the machine readable instructions comprise a programfor execution by a processor such as the processor 1312 shown in theexample processor platform 1300 discussed below in connection with FIG.13. The program may be embodied in software stored on a tangiblecomputer readable storage medium such as a CD-ROM, a floppy disk, a harddrive, a digital versatile disk (DVD), a Blu-ray disk, or a memoryassociated with the processor 1312, but the entire program and/or partsthereof could alternatively be executed by a device other than theprocessor 1312 and/or embodied in firmware or dedicated hardware.Further, although the example program is described with reference to theflowchart illustrated in FIG. 9, many other methods of implementing theexample power detector 410 may alternatively be used. For example, theorder of execution of the blocks may be changed, and/or some of theblocks described may be changed, eliminated, or combined.

The program of FIG. 9 begins with an initiation of the power detector410 of FIGS. 4 and/or 5 (e.g., the power detector 410 is powered on,connected to a meter such as the meters 408, 420, receives user input,etc.). At block 910, the power sensor 502 measures a magnetic field neara power cord, such as the power cord 100 of FIG. 4, of a device, such asthe media presentation device 402. At block 920 the environment sensor504 measures the environment magnetic field. Block 920 may occur before,after, or at the same time as block 910. The example power sensor 502measures a magnetic field (block 910) as described below in connectionwith FIG. 10. Additionally, the example environment sensor 504 measuresa magnetic field (block 920) as described below in connection with FIG.10.

At block 930 of FIG. 9, the example comparator 506 compares the magneticfield measurements from block 910 and block 920. In some examples, thecomparator 506 performs calibration of the magnetic field measurementsbased on the physical orientation of the power sensor 502 and/or thephysical orientation of the environment sensor 504. In some examples,the example comparator 506 subtracts the environment magnetic fieldmeasurement taken in block 920 from the measurement of the magneticfield near the power cord taken in block 910. At block 940, thecomparator 506 determines a resultant magnetic field representative ofthe magnetic field induced by the power cord 100 of an example device.For example, the comparator 506 calculates one or more vector(s) fromthe compared magnetic field measurement components of the magneticfields measured in blocks 910, 920.

At block 950 of FIG. 9, the example status analyzer 510 determines anoperational status of the example device based on the determined devicemagnetic field vector. In some examples, the status analyzer 510determines the operational status (e.g., powered on, powered off onstandby, in sleep mode, etc.) of a device based on a magnitude of thedevice magnetic field vector satisfying one or more thresholds.Accordingly, thresholds may be used to determine the operational statuswhen the magnitude is between a plurality of thresholds. The examplethresholds may be determined when setting up (or calibrating the powerdetector 410). For example, the media presentation device 402 may be setto a plurality of operational states (e.g., powered off, powered on, onstandby, in sleep mode, etc.), and the comparator 506 determines thedevice magnetic field for when the media presentation is in theplurality of states. Accordingly, from the determined device magneticfield measurements, the status analyzer 510 may assign the appropriatethresholds (e.g., within a designated range (or percentage to allow forerror) of the measured magnetic field strength for the correspondingoperational states). As an example, the status analyzer 510 maydetermine that the corresponding operational status is powered off whenthe magnitude is less than a sleep threshold, is in sleep mode when themagnitude is less than a stand by threshold, on standby when themagnitude is less than a powered on threshold, and powered on when themagnitude is greater than the powered on threshold. In some examples,the status analyzer 510 uses predefined thresholds for the mediapresentation device 402. Accordingly, the thresholds may be predefinedfor certain types of media presentation device (e.g., based onmanufacture, model, device type, etc.).

In the illustrated example of FIG. 9, at block 960, the status analyzer510 provides the operational status information to a meter (e.g., themeters 408, 420) or other device communicatively coupled with the powerdetector 410. At block 970, the power detector 410 determines whether tocontinue detecting the operational status of the device under test. Ifthe power detector 410 is to continue detecting the operational statusof the device, control returns to block 910 and/or block 920 (e.g., atime period of analyzing the device under test has not expired,instructions from a meter indicate that analysis is to continue, userinstructions indicate that analysis is to continue, etc.). If the powerdetector 410 is not to continue detecting the operational status of thedevice (e.g., a time period of analyzing the device under test hasexpired, the power detector 110 is shutdown or powered off, etc.), theprogram 900 ends.

A flowchart representative of example machine readable instructions forimplementing the power sensor 502 and/or the environment sensor 504 ofFIG. 5 is shown in FIG. 10. In this example, the machine readableinstructions comprise a program for execution by a processor such as theprocessor 1312 shown in the example processor platform 1300 discussedbelow in connection with FIG. 13. The program may be embodied insoftware stored on a tangible computer readable storage medium such as aCD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), aBlu-ray disk, or a memory associated with the processor 1312, but theentire program and/or parts thereof could alternatively be executed by adevice other than the processor 1312 and/or embodied in firmware ordedicated hardware. Further, although the example program is describedwith reference to the flowchart illustrated in FIG. 10, many othermethods of implementing the example power sensor 502 and/or the exampleenvironment sensor 504 may alternatively be used. For example, the orderof execution of the blocks may be changed, and/or some of the blocksdescribed may be changed, eliminated, or combined.

The program 1000 of FIG. 10 beings with an initiation of the powersensor 502 and/or the environment sensor 504. At block 1010, the powersensor 502 and/or the environment sensor 504 measure three dimensionalcomponents of a magnetic field around the power sensor 502 and/or theenvironment sensor 504. At block 1020, the power sensor 502 and/or theenvironment sensor 504 computes a magnetic field vector from the 3Dcomponents (e.g., the components 602 (x, y, z)). At block 1030, thesensor determines the magnitude of the field vector based on thedetermined 3D components.

A flowchart representative of example machine readable instructions forimplementing the comparator 506 of FIGS. 5 and/or 8 is shown in FIG. 11.In this example, the machine readable instructions comprise a programfor execution by a processor such as the processor 1312 shown in theexample processor platform 1300 discussed below in connection with FIG.13. The program may be embodied in software stored on a tangiblecomputer readable storage medium such as a CD-ROM, a floppy disk, a harddrive, a digital versatile disk (DVD), a Blu-ray disk, or a memoryassociated with the processor 1312, but the entire program and/or partsthereof could alternatively be executed by a device other than theprocessor 1312 and/or embodied in firmware or dedicated hardware.Further, although the example program is described with reference to theflowchart illustrated in FIG. 11, many other methods of implementing theexample comparator 506 may alternatively be used. For example, the orderof execution of the blocks may be changed, and/or some of the blocksdescribed may be changed, eliminated, or combined.

The program 1100 of FIG. 11 begins with an initiation of the examplecomparator 506 of FIG. 5 (e.g., in response to receiving measurementsand/or measurement samples from the power sensor 502 and/or environmentsensor 504). At block 1110, the subtractor 810 subtracts environmentmagnetic field measurement samples (received from the environmentsensor) from power cord magnetic field measurement samples (receivedfrom the power sensor 502) to determine device magnetic fieldmeasurement samples. In some examples, at block 1110 the subtractor 810calculates an average value of each sample period determined from thedevice magnetic field measurement samples. If a non-zero average isfound (i.e., a DC field is detected), the sample harmonizer 830subtracts the non-zero average from the sample periods to obtain ACfield sample periods.

At block 1130 of the illustrated example of FIG. 11, the sampleharmonizer 830 performs a filtering and averaging of the samples. Theexample sample harmonizer 830 averages each sample from a sample periodwith the corresponding samples from the other remaining periods. Forexample, for 50 Hz or 60 Hz AC, with 99 samples taken by the powersensor 502 and the environment sensor 504, the sample harmonizer 830averages 11 sample values from each of the determined 9 sample periods(and/or averages each sample for each axis (x, y, z)).

At block 1140, the RMS calculator 840 performs an RMS calculation overthe device magnetic field measurement vector for each dimension of themulti-dimensional sample measurement. The RMS calculator 840 determinesthe magnitude of the determined device magnetic field vector. At block1150, the measurement output 1150 outputs the device magnetic fieldmeasurement information to the status analyzer 510. After block 1150,the program 1100 ends.

As mentioned above, the example processes of FIGS. 9, 10, and/or 11 maybe implemented using coded instructions (e.g., computer and/or machinereadable instructions) stored on a tangible computer readable storagemedium such as a hard disk drive, a flash memory, a read-only memory(ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, arandom-access memory (RAM) and/or any other storage device or storagedisk in which information is stored for any duration (e.g., for extendedtime periods, permanently, for brief instances, for temporarilybuffering, and/or for caching of the information). As used herein, theterm tangible computer readable storage medium is expressly defined toinclude any type of computer readable storage device and/or storage diskand to exclude propagating signals and to exclude transmission media. Asused herein, “tangible computer readable storage medium” and “tangiblemachine readable storage medium” are used interchangeably. Additionallyor alternatively, the example processes of FIGS. 9, 10, and/or 11 may beimplemented using coded instructions (e.g., computer and/or machinereadable instructions) stored on a non-transitory computer and/ormachine readable medium such as a hard disk drive, a flash memory, aread-only memory, a compact disk, a digital versatile disk, a cache, arandom-access memory and/or any other storage device or storage disk inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, for brief instances, for temporarily buffering,and/or for caching of the information). As used herein, the termnon-transitory computer readable medium is expressly defined to includeany type of computer readable storage device and/or storage disk and toexclude propagating signals and to exclude transmission media. As usedherein, when the phrase “at least” is used as the transition term in apreamble of a claim, it is open-ended in the same manner as the term“comprising” is open ended.

FIG. 12 is a block diagram of an example processor platform 1300 capableof executing the instructions of FIGS. 9, 10, and/or 11 to implement thepower detector 410 of FIGS. 4 and/or 5 and/or the comparator 506 of FIG.8. The processor platform 1200 can be, for example, a server, a personalcomputer, a mobile device (e.g., a cell phone, a smart phone, a tabletsuch as an iPad™), a personal digital assistant (PDA), an Internetappliance, a DVD player, a CD player, a digital video recorder, aBlu-ray player, a gaming console, a personal video recorder, a set topbox, or any other type of computing device.

The processor platform 1200 of the illustrated example includes aprocessor 1212. The processor 1212 of the illustrated example ishardware. For example, the processor 1212 can be implemented by one ormore integrated circuits, logic circuits, microprocessors or controllersfrom any desired family or manufacturer.

The processor 1212 of the illustrated example includes a local memory1213 (e.g., a cache). The processor 1212 of the illustrated example isin communication with a main memory including a volatile memory 1214 anda non-volatile memory 1216 via a bus 1218. The volatile memory 1214 maybe implemented by Synchronous Dynamic Random Access Memory (SDRAM),Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory(RDRAM) and/or any other type of random access memory device. Thenon-volatile memory 1216 may be implemented by flash memory and/or anyother desired type of memory device. Access to the main memory 1214,1216 is controlled by a memory controller.

The processor platform 1200 of the illustrated example also includes aninterface circuit 1220. The interface circuit 1220 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 1222 are connectedto the interface circuit 1220. The input device(s) 1222 permit(s) a userto enter data and commands into the processor 1212. The input device(s)can be implemented by, for example, an audio sensor, a microphone, acamera (still or video), a keyboard, a button, a mouse, a touchscreen, atrack-pad, a trackball, isopoint and/or a voice recognition system.

One or more output devices 1224 are also connected to the interfacecircuit 1220 of the illustrated example. The output devices 1224 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay, a cathode ray tube display (CRT), a touchscreen, a tactileoutput device, a light emitting diode (LED), a printer and/or speakers).The interface circuit 1220 of the illustrated example, thus, typicallyincludes a graphics driver card, a graphics driver chip or a graphicsdriver processor.

The interface circuit 1220 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodem and/or network interface card to facilitate exchange of data withexternal machines (e.g., computing devices of any kind) via a network1226 (e.g., an Ethernet connection, a digital subscriber line (DSL), atelephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 1200 of the illustrated example also includes oneor more mass storage devices 1228 for storing software and/or data.Examples of such mass storage devices 1228 include floppy disk drives,hard drive disks, compact disk drives, Blu-ray disk drives, RAIDsystems, and digital versatile disk (DVD) drives.

The coded instructions 1232 of FIGS. 9, 10, and/or 11 may be stored inthe mass storage device 1228, in the volatile memory 1214, in thenon-volatile memory 1216, and/or on a removable tangible computerreadable storage medium such as a CD or DVD.

From the foregoing, it will be appreciated that the above disclosedmethods, apparatus and articles of manufacture determine an operationalstatus of a device based on a measured magnetic field associated withthe device. In examples disclosed herein, sensors performmulti-dimensional measurement of magnetic fields surrounding a powercord attached to the device. Multi-dimensionally measuring examplemagnetic fields surrounding a device allows for freedom of positioningthe sensors such that, for example, distorted magnetic fields (e.g.,caused by one or more twist(s) in the power cord) can be measured.Examples disclosed herein allow for increased accuracy in measuring adevice magnetic field by accounting for environment magnetic fields thatmay affect measurement of a device magnetic field by measuring theenvironment magnetic field and comparing the environment magnetic fieldto a magnetic field measured near a power cord of a device.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent.

What is claimed is:
 1. A method comprising: determining, with aprocessor, a first multi-dimensional measurement of a first magneticfield generated by a power cord to supply power to a device; anddetermining, via the processor, an operational status of the devicebased on the first multi-dimensional measurement.
 2. A method accordingto claim 1, further comprising: determining a second multi-dimensionalmeasurement of a second magnetic field of an environment of the device,wherein determining the operational status comprises comparing the firstmulti-dimensional magnetic field measurement and the secondmulti-dimensional magnetic field measurement.
 3. A method according toclaim 2, wherein comparing the first multi-dimensional magnetic fieldmeasurement and the second multi-dimensional magnetic field measurementcomprises subtracting the second multi-dimensional measurement from thefirst multi-dimensional measurement to determine a device magnetic fieldvector.
 4. A method according to claim 3, wherein determining theoperational status of the device comprises comparing a magnitude of thedevice magnetic field vector to a threshold.
 5. A method according toclaim 2, wherein the first magnetic field is measured at a firstlocation and the second magnetic field is measured at a second location,the first location being closer to the power cord than the secondlocation.
 6. A method according to claim 5, wherein the power cord is tosupply electricity to the device, the electricity causing a devicemagnetic field included in the first magnetic field, and wherein thesecond location is a distance from the power cord so that the secondmagnetic field essentially does not include the device magnetic field.7. A method according to claim 1, wherein the operational statuscomprises one of powered on, on standby, in sleep mode, or powered off.8. An apparatus comprising: a first sensor to measure a first magneticfield associated with a device in at least three dimensions; a statusanalyzer to determine an operational status of the device based on themeasurement of the first sensor.
 9. An apparatus according to claim 8, asecond sensor to measure a second magnetic field, the status analyzer todetermine the operational status by comparing the measurement of thefirst magnetic field and the measurement of the second magnetic field.10. An apparatus according to claim 9, wherein the first sensor is todevelop a first multi-dimensional measurement of the first magneticfield, and the second sensor is to develop a second multi-dimensionalmeasurement of the second magnetic field.
 11. An apparatus according toclaim 10, wherein the status analyzer is to subtract the secondmulti-dimensional measurement from the first multi-dimensionalmeasurement to determine a device magnetic field vector.
 12. Anapparatus according to claim 11, wherein the status analyzer is todetermine the operational status of the device by comparing a magnitudeof the device magnetic field vector to a threshold.
 13. An apparatusaccording to claim 9, wherein the first sensor is located at a firstlocation and the second sensor is located at a second location, thefirst location being closer to a wire attached to the first device thanthe second location.
 14. An apparatus according to claim 13, wherein thewire is to supply electricity to the device to cause a device magneticfield included in the first magnetic field, and the second location is adistance from the wire so that the second magnetic field essentiallydoes not include the device magnetic field.
 15. An apparatus accordingto claim 8, wherein a first orientation of the first sensor and a secondorientation of the second sensor are identical relative to the devicewire.
 16. An apparatus according to claim 8, wherein the operationalstatus comprises one of powered on, on standby, in sleep mode, orpowered off.
 17. A tangible machine readable storage medium comprisinginstructions that, when executed, cause a machine to at least: determinea first multi-dimensional measurement of a first magnetic fieldgenerated by a power cord to supply power to a device; and determine anoperational status of the device based on the first multi-dimensionalmeasurement.
 18. A storage medium according to claim 17, wherein theinstructions, when executed, further cause the machine to: determine asecond multi-dimensional measurement of a second magnetic field of anenvironment of the device, and determine the operational status bycomparing the first multi-dimensional magnetic field measurement and thesecond multi-dimensional magnetic field measurement.
 19. A storagemedium according to claim 18, wherein the instructions, when executed,cause the machine to compare the first magnetic field and the secondmagnetic field by subtracting the second multi-dimensional measurementfrom the first multi-dimensional measurement to determine a devicemagnetic field vector.
 20. A storage medium according to claim 19,wherein the instructions, when executed, cause the machine to determinethe operational status of the device by comparing a magnitude of thedevice magnetic field vector to a threshold.
 21. A storage mediumaccording to claim 20, wherein the instructions, when executed, causethe machine to: measure the first magnetic field at a first location;and measure a second magnetic field at a second location, the firstlocation being closer to the power cord than the second location.
 22. Astorage medium according to claim 21, wherein the power cord is tosupply electricity to the device to cause a device magnetic fieldincluded in the first magnetic field, and wherein the second location isa distance from the wire so that the second magnetic field essentiallydoes not include the device magnetic field.
 23. A storage mediumaccording to claim 17, wherein the operational status comprises one ofpowered on, on standby, in sleep mode, or powered off.